Abstract P2-16-06: Protein expression and subcellular localization of a clathrin adaptor AP-1 associate with tumor growth activity in breast cancer
Authors: Nobuhiro Hoshi, Kazunoshin Tachibana, Takefumi Uemura, Yuko Nishimagi, Masaru Noda, Maiko Okano, Sadahiko Abe, Tohru Otake, Satoshi Waguri
Journal: Cancer Research (2023)

Abstract [Introduction] Breast cancer is the fifth leading cause of cancer-related death among women, and its prevalence is the highest in all cancers of Japanese women. To improve the prognosis of breast cancer patients, new diagnostic and therapeutic tools need to be developed. Adaptor protein complex-1 (AP-1) is one of the clathrin adaptor molecules regulating intracellular transport of specific cargos between the trans-Golgi network (TGN) and endosomes. Although the detailed mechanisms have been poorly elucidated, previous reports suggest that AP-1 expression is related with cell proliferation and cancer metastasis. The purpose of this study is to investigate the association between AP-1 expression in tumor tissue measured with immunohistological analyses and surrogate markers of cancer aggressiveness, such as Ki-67 labeling index and/or breast cancer subtypes. [Materials and methods] The records of 207 primary breast cancer patients surgically treated at Fukushima Medical University Hospital from 2011 to 2014 were reviewed. Paraffin embedded sections of these patients were processed for immunohistochemistry examination using antibody against γ-adaptin, a subunit of AP-1, and then its immunoreactivity was quantified. The staining patterns were also graded into 4 grade: Negative (Neg) = 1, Perinuclear (PN) = 2, Scattered (Sc) = 3, and Diffuse (Dif) = 4. The association of the stain characteristics, such as intensity and patterns, and clinicopathological factors, including Ki-67 labelling index and tumor subtypes, were assessed. In addition, the detailed intracellular localization of AP-1 was examined with double immunofluorescence microscopy using markers for the TGN and endosome. [Results] AP-1 intensity was associated with Ki-67 index (p &amp;lt; 0.005) and subtypes (p &amp;lt; 0.0001). Patients with high Ki-67 index showed significantly higher AP-1 intensity than those with low Ki-67 index (p &amp;lt; 0.05). Regarding the tumor subtypes, HER2 type (p &amp;lt; 0.001) and TNBC (p &amp;lt; 0.05) showed significantly higher AP-1 intensity than Luminal A. HER2 type also showed significantly higher AP-1 intensity than Luminal B (p &amp;lt; 0.01). In terms of the staining pattern, AP-1 distribution was also significantly associated with Ki-67 index (p &amp;lt; 0.0001) and subtype (p &amp;lt; 0.0001). The staining pattern grade of high Ki-67 index patients was significantly higher (p &amp;lt; 0.0001) than that of low Ki-67 index patients. Regarding the association with subtypes, the grades in Luminal B (p &amp;lt; 0.0001), HER2 type (p &amp;lt; 0.0001), and TNBC (p &amp;lt; 0.005) were significantly higher than that of Luminal A, and HER2 type also showed higher score than Luminal B (p &amp;lt; 0.01). In tumor cells with Sc pattern, AP-1 was mainly localized in EEA1-positive endosomes, but the localization in TGN was not apparent. [Conclusion] Although further confirmative studies are needed, these results suggest that the protein expression and the endosomal localization of AP-1 are likely related to the cellular proliferation activity in breast cancer tissues. Aberrant AP-1 distribution could be a predictive marker of the tumor growth potential. Citation Format: Nobuhiro Hoshi, Kazunoshin Tachibana, Takefumi Uemura, Yuko Nishimagi, Masaru Noda, Maiko Okano, Sadahiko Abe, Tohru Otake, Satoshi Waguri. Protein expression and subcellular localization of a clathrin adaptor AP-1 associate with tumor growth activity in breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-16-06.